This section is intended to introduce various aspects of the art, which may be associated with embodiments of the disclosed techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the disclosed techniques. Accordingly, it should be understood that this section is to be read in this light, and not necessarily as admissions of prior art.
Three-dimensional (3D) model construction and visualization have been widely accepted by numerous disciplines as a mechanism for analyzing, communicating, and comprehending complex 3D datasets. Examples of structures that can be subjected to 3D analysis include the earth's subsurface, facility designs and the human body, to name just three examples.
The ability to easily interrogate and explore 3D models is one aspect of 3D visualization. Relevant models may contain both 3D volumetric objects and co-located 3D polygonal objects. Examples of volumetric objects include seismic volumes, MRI scans, reservoir simulation models, and geologic models. Interpreted horizons, faults and well trajectories are examples of polygonal objects. In some cases, it may be desirable to view the volumetric and polygonal objects concurrently to understand their geometric and property relations. If every cell of the 3D volumetric object is rendered fully opaque, other objects in the scene will of necessity be occluded, and so it becomes advantageous at times to summarize the properties assigned to such volumetric objects, using various aggregation techniques such as summing or averaging, onto cubes, spheres, or surfaces so that other objects may be seen. These 3D model interrogation and exploration tasks are important during exploration, development and production phases in the oil and gas industry. Similar needs exist in other industries.
3D volumetric objects may be divided into two basic categories: structured grids and unstructured grids. Those of ordinary skill in the art will appreciate that other types of grids may be defined on a spectrum between purely structured grids and purely unstructured grids. Both structured and unstructured grids may be rendered for a user to explore and understand the associated data. There are large numbers of known volume summarization techniques for structured grids.
One known way to view and interrogate a 3D volume is to render summarized volumetric properties on a surface using summation or averaging methods, commonly called a property or attribute map. The map may be rendered on an arbitrary surface. In the case of a structured grid, such as seismic or a medical scan, the user can create an average property map along one of the primary directions: XY (inline or axial), XZ (cross-line or coronal) and YZ (time slice or sagital). Alternatively, a map can be created on any surface, horizon, or layer within the 3D volume. The organization of the grid, in many instances, provides for easy indexing of individual grid cells and, therefore, provides for rapid map creation. A typical benefit of maps created on similar surfaces is the ability to quickly compare summary information between multiple models possessing either similar or widely different gridding styles.
Some 3D visualization techniques are suitable for grid structures that fall between fully structured grids and fully unstructured grids. One such visualization technique relates to the use of reservoir simulation grids based on geologic models.
A geologic model may be thought of as an intermediate step between completely structured and completely unstructured grids. In its simplest form, a geologic model may comprise a structured grid with deformed geometry. In a geologic model, cells may be uniquely addressable, but their geometries are not entirely implicit. Because of deformation, corner vertices of a cell cannot be calculated from just the grid origin and unit vectors along with the cell's indices. However, each cell does comprise a polyhedron with six faces. An index may be used to find its neighbors. Each cell (except the boundary faces) shares six faces with other cells, and shares eight corners with other cells. Neighboring cells sharing a vertex may also be addressed. Those of ordinary skill in the art will appreciate that there may be variations on this basic definition of a geologic model. For example, a geologic model may comprise keyed out cells, faults and pinch out cells. However, the basic indices still apply and the majority of cells comprise six-faced polyhedrons. In addition, reservoir simulation grids that are based on geologic models may retain (i, j, k) cell indices, while explicitly storing cell geometries.
When attempting to produce a property map on an unstructured grid having inactive cells, the resulting display can be adversely impacted by the presence of inactive cells at the top or bottom of models with non-vertical columns of cells. Significant occlusion or overlap of regions frequently occurs around these cells, for grids with curvature or that are deviated to faults, as a result of the vertical projection from multiple z-values and overlap of adjacent cells. Furthermore, maps created as a projection onto a flat surface don't represent the actual topology of the model.
U.S. Pat. No. 6,574,566 to Grismore, et al. relates to a method for recognizing and comparing features of attribute data expressed in a 3D data survey. The method involves: extracting, mapping, color coding and displaying 3D data for at least one attribute. The data is based on tomographic paths. The tomographic paths are defined within a subvolume of instantaneous attribute data having the shape of a sphere. This is accomplished by extracting the subvolume of attribute data having a desired shape, defining multiple tomographic paths extending from a point within the subvolume to its bounding surface, combining instantaneous attribute values encountered along each of the tomographic paths to determine multiple aggregate values, mapping the thus determined aggregate attribute values on the surface of the sphere using a color code, and displaying the color coded sphere. The attribute maps are correlated with preexisting geological or stratigraphic templates to identify features.
U.S. Pat. No. 7,451,066 to Edwards, et al., describes a “near wellbore modeling” software that, when executed by a processor of a computer, will model a localized area of a reservoir field which surrounds and is located near a specific wellbore in the reservoir field. In a disclosed method, input data representative of a reservoir field containing a plurality of wellbores is received. A boundary around one specific wellbore is established in the reservoir field which will be individually modeled and simulated. A “fine scale” unstructured grid is imposed inside the boundary consisting of a plurality of tetrahedrally shaped grid cells and further impose a fine scale structured grid about the perforated sections of the specific wellbore. A plurality of fluxes/pressure values at the boundary is determined, the fluxes/pressure values representing characteristics of the reservoir field located outside the boundary. One or more properties are established for each tetrahedral cell of the unstructured grid and each cylindrical grid cell of the structured grid. A simulation is run using the fluxes/pressure values at the boundary to mimic the reservoir field outside the boundary and using the fine scale grid inside the boundary to thereby determine a plurality of simulation results corresponding respectively to the plurality of grid cells located inside the boundary the plurality of simulation results being representative of a set of characteristics of the reservoir field located inside the boundary. The plurality of simulation results which characterize the reservoir field located inside the boundary is displayed. By coarsening the grid inside the boundary, a structured grid outside the boundary is imposed. A simulation of the entire reservoir field may then be redone.
U.S. Pat. No. 6,106,561 to Farmer discloses a Flogrid Simulation Gridding Program that includes a Flogrid structured gridder. The structured gridder includes a structured areal gridder and a block gridder. The structured areal gridder may build an areal grid on an uppermost horizon of an earth formation by performing a disclosed method. The disclosed method comprises building a boundary enclosing one or more fault intersection lines on the horizon and building a triangulation that absorbs the boundary and the faults. A a vector field is built on the triangulation. A web of control lines and additional lines is built inside the boundary. The web of control lines and additional lines have a direction that corresponds to the direction of the vector field on the triangulation thereby producing an areal grid. The areal grid is post-processed so that the control lines and additional lines are equispaced or smoothly distributed. The block gridder of the structured gridder drops coordinate lines down from the nodes of the areal grid to complete the construction of a three dimensional structured grid. A reservoir simulator receives the structured grid and generates a set of simulation results which are displayed on a 3D viewer for observation by a workstation operator.
U.S. Pat. No. 6,078,869 to Gunasekera describes a Petragrid method and apparatus that generates grid cell property information that is adapted for use by a computer simulation apparatus. A disclosed interpretation workstation includes at least two software programs stored therein: a first program called “Petragrid” and a second simulation program for generating a set of simulation results for display. The first Petragrid software program will receive well log and seismic data which indicates each layer of a formation grid, each layer of the formation where the grid is comprised of a plurality of cells. Accurate data associated with each grid cell, such as the transmissibility, is generated. Accurate data for each cell will be transmitted to the second simulation program which will respond by generating a set of more accurate simulation results for each cell of the grid and overlaying the more accurate simulation result for each cell onto each of the corresponding cells of the grid being displayed on the workstation display by the Petragrid software. The workstation will display each layer of the formation where each layer is gridded and each grid cell has its own color corresponding in numerical value to a more accurate simulation result (e.g. pressure or saturation) that corresponds to that cell.
U.S. Pat. No. 6,826,520 to Khan, et al., discloses a method for scaling up permeabilities associated with a fine-scale grid of cells representative of a porous medium to permeabilities associated with an unstructured coarse-scale grid of cells representative of the porous medium. An aerially unstructured Voronoi computational grid is generated using the coarse-scale grid as the genesis of the computational grid. The computational grid is then populated with permeabilities associated with the fine-scale grid. Flow equations are developed for the computational grid the flow equations are solved and inter-node fluxes and pressure gradients are then computed for the computational grid. These inter-node fluxes and pressure gradients are used to calculate inter-node average fluxes and average pressure gradients associated with the coarse-scale grid. The inter-node average fluxes and average pressure gradients associated with the coarse grid are then used to calculate upscaled permeabilities associated with the coarse-scale grid.
U.S. Patent Application Publication No. 2009/0303233 to Lin, et al. describes a system and method for probing geometrically irregular grids. The disclosure specifically relates to systems and methods for imaging a 3D volume of geometrically irregular grid data. Various types of probes and displays are used to render the geometrically irregular grid data, in real-time, and analyze the geometrically irregular grid data. The grids described require topologically regular i,j,k indexing. In this disclosed system, the 3D volume is defined as:cell=f(I,J,K)=(v1,v2 . . . v8,a1,a2 . . . an)where v1, v2 . . . and v8 are eight vertices for the cells and an are attributes. This indexing is a requirement for the described probing technique, which significantly limits the types of data on which the described method can operate.
EP Patent Application Publication No. 1865343 to Gunning, et al., describes a method for estimating and/or reducing uncertainty in reservoir models of potential petroleum reservoirs. The method comprises receiving the results of a stochastic seismic inversion and transforming the inversion data into a form suitable for reservoir modeling and flow simulations while honoring inter-property and inter-layer correlations in the inversion data as well as measured well data and other geological constraints.